Symptoms of grief lasting for more than two weeks may be diagnosed as depression.

Photograph: Alamy

She was a tearful, older woman holding a bulging bin liner. Community pharmacies are collection points for society's redundant medicines, and the bin liner – her late husband's medical legacy and stark testament to over-prescribing – was dispatched for disposal. I listened as she reflected on how empty, her life had suddenly become. She needed help sleeping. I gave her maximum bedtime doses of an antihistamine known to cause drowsiness.

The funeral was a month since, and her continued grieving would seem normal and necessary. But, in fact, a major reappraisal is under way.

The revised Diagnostic and Statistical Manual of Mental Disorders (DSM-5), scheduled for publication in May 2013 by the American Psychiatric Association (APA), proposes that grief reactions of more than two weeks may be diagnosed as depression. And where DSM leads, the rest follow. The World Health Organisation's international classification of diseases group is debating the creation of a new illness – prolonged grief disorder.

Crucially, once a behaviour has been labelled as an illness, it becomes a legitimate target for treatment by Big Pharma. The transformation of bereavement into a mental disorder will create a new global market for antidepressant therapy. And a recent critical Lancet editorial describing such transformation as diagnostically simplistic and therapeutically flawed, will present little obstacle.

Grief can affect us all; depressive illness only those who are cursed with it. So while grief must be allowed to run its course, any associated major depression must not be normalised. Superficially, symptoms may be similar, and diagnoses can slip and slide. It is in boundary issues such as this where medicalisation preys on normality, and DSM-5 has many such planning applications.

They include the proposal that the term dementia be dropped, adding a new disease entitled neurocognitive disorder, and that Alzheimer's disease be reclassified into biochemical sub-groups. By transforming facets of ageing, such as confusion and memory loss, into apparently treatable biological disorders, not only does an ever-increasing number of older people become legitimate targets for drug treatment but the entire issue of the ageing population is reframed in a medicobiological context. Needless to say, the financial reward for the medicalisation of old age is the stuff of dreams for giant pharmaceutical companies.

Also under scrutiny by DSM-5 is children's mental health. The boundaries defining attention deficit hyperactive disorder are to be redrawn, and a new disorder – disruptive mood dysregulation disorder, characterised by disproportional recurrent temper tantrums – is to be created. When the boundaries of illness classification are redrawn they are inevitably broadened. So more children will be labelled as mentally ill, with the lifelong harm that can do to child and family, and the market for drug treatment – amphetamines and methylphenidate – will expand accordingly.

The continued association of increased drug company sales with DSM-5 revisions has inevitably led to accusations of undue corporate influence within APA. According to a study by Lisa Cosgrove and colleagues from the ethics centre at Harvard University, 69% of the DSM-5 taskforce members have financial ties to the pharmaceutical industry, and the panels with members on them that have the most conflicts of interest are those for which drug treatment is the first-line intervention, to the extent that 11 of the 12 panel members for psychotic disorders, and all of the panel for restless legs syndrome, have ties to the drug companies that manufacture the respective treatments.

The promotion of drugs in relation to normal human behaviour has been innovatively investigated highlighted in the satirical work of Justine Cooper, on a spoof website that markets the drug, Avafynetyme.

The opening statement of Ivan Illich's 1975 publication Medical Nemesis was: "The medical establishment has become a major threat to health." Today, medicalisation of normal behaviour is a globally important contributor to over-prescribing and iatrogenic harm. But to gauge its local impact, you need only ask your pharmacist how many bin liners they've accepted this week.